This invention relates to a method and apparatus utilizing X-rays, or other penetrating radiation, to examine a body for the purpose of producing pictures or other graphic displays revealing details of internal body parts, and deals more particularly with such a method and apparatus wherein a body is examined through the use of a narrow beam of rays moved in a scanning motion relative to the body to measure the transmissivity of the body along a large number of straight line paths passing through the body and which transmissivity measurements are then used to compose a point-by-point picture or other graphic display.
A long known and common way of examining a body by means of X-rays is to subject a relatively wide area of the body to a field of X-rays and to expose a photographic film to those rays which rays pass through the body and exit from its other side. Generally, the film used in this procedure has a very high contrast ratio so as to display differences in the X-ray density of a particular tissue, organ, or other object being studied. As a result, information which falls outside the dynamic range of the film is lost. For example, it is almost completely impossible with this method to view both soft tissue and bone in the same X-ray photograph because of their significantly different average densities or X-ray absorption and transmissivity coefficients. Thus, to investigate body parts located in the same portion of the body but having different densities it is normally necessary to take a number of exposures of the same area at different levels of X-ray intensity, thereby undesirably increasing the patient's X-ray dosage.
More recently, various different scanning systems utilizing X-rays have been developed for body examination. These systems usually use a detector whose dynamic range is larger than that of X-ray films and, as a consequence, these systems are generally capable of producing pictures or other displays having much more detail or definition than that provided by photographic films. Often, the improvement provided by such scanning systems is such as to allow body studies to be made without resort to the use of dyes and similar media which are often used to enhance X-ray photographs and which can produce a discomfort and danger to the patient. Also, in a scanning system, the body area examined is investigated point-by-point and the information obtained during the course of a scan may be converted to digital form and computer processed through various techniques, such as some developed by space-photography scientists, to enhance the final image in a number of different ways, as for example, to remove background noise, unwanted features, scanning defects, and the like.
However, regardless of the ability to use computer-enhancement algorithms and techniques to improve the data furnished by X-ray scanning systems, the dynamic limitations of the detectors used in such systems ultimately limit the range and resolutions of the system, as far as its ability to produce good detail and definition over a very wide range of X-ray densities and thicknesses of flesh, bone, organ, tumor, fat and other body material is concerned.
The general object of this invention, therefore, is to provide a system, and related method, for examining a body by X-rays or similar penetrating radiation which system is an improvement on presently known scanning-type systems, particularly insofar as having an extremely wide dynamic range enabling the production of pictures or other graphic displays having high resolution and clear detail. Because of this extremely wide dynamic range the output of the system of the invention is vastly improved in its information content, and therefore enhancement techniques are much more effective and allow a better application of enhancement algorithms.
Another important object of this invention is to provide an apparatus and method of the foregoing character wherein the radiation dose received by the patient during the examination may be held to an absolute minimum. In particular, the system operates to hold constant the intensity of the radiation detected by the detector by varying the emitted or body-incident radiation. Since the detector can operate at a very low level of detected intensity, body-incident radiation need only be sufficient to maintain such low detected level. Also, since the useful range of the system is very great, the information derived from a single scan may be processed to produce a number of different pictures each viewing body parts having different X-ray densities. That is, computer programs associated with this system will allow any density range to be examined and enhanced or rejected in the resulting picture or display.
In the system of the invention a body-incident beam of radiation is dynamically varied, either in intensity or in both intensity and wavelength as the beam, because of its scanning motion, encounters regions of differing transmissivity or X-ray density to keep the body-exiting radiation at a constant intensity. Basically, as the transmissivity of the beam path through the body decreases the intensity of the body-incident beam is increased. The body-incident beam intensity is the only factor varied in accordance with one embodiment of the invention. In accordance with another embodiment of the invention, the mean wavelength of the beam is varied along with the body-incident beam intensity and in such a manner that the wavelength is shortened as the intensity is increased. That is, softer X-rays are used when going through softer or less X-ray dense tissue and harder X-rays are used when going through harder or more X-ray dense tissue. This can be used to advantage in some cases to bring out still more detail in the resulting picture or other display.
Other objects and advantages of the invention will be apparent from the following description and from the drawings forming apart hereof.